An organic electroluminescence device may be classified into a bottom-emitting type and a top-emitting type and may also be classified into an active matrix type having a pixel driving circuit in each pixel and a passive matrix type. Where the organic electroluminescence device is a bottom-emitting type, as well as an active matrix type, the pixel driving circuit and various kinds of wiring for applying voltages to the pixel driving circuit may take up space in a pixel, and an aperture ratio may be restricted. Accordingly, in order to improve the aperture ratio, the top-emitting type is introduced.
In the top-emitting type organic electroluminescence device, a conductive material having improved reflection characteristics and a suitable work function may be used for a pixel electrode. However, currently there isn't any applicable single material that satisfies such characteristics. Therefore, in order to satisfy the characteristics of the pixel electrode of the top-emitting type organic electroluminescence device, a multi-layered structure is adopted to the pixel electrode.
Korean patent application No. 2000-0058739 discloses an organic electroluminescence device of a top-emitting type. The organic electroluminescence device comprises a substrate, a reflecting plate formed on a top surface of the substrate, a first electrode formed on the top surface of the reflecting plate, an emitting layer formed on a top surface of the first electrode, and a second electrode formed on the emitting layer. Thus, by forming the reflecting plate on the top surface of the substrate, a structure in which the light emitted from the emitting layer is reflected to the opposite direction of the substrate, that is, the top-emitting type organic electroluminescence device is embodied.
FIG. 1 is a cross-sectional view of a method of fabricating an top-emitting type organic electroluminescence device employing a multi-layered pixel electrode according to the prior art.
Referring to FIG. 1, a first pixel electrode film and a second pixel electrode film are successively formed on a substrate 10. A photoresist pattern 95 is formed on the second pixel electrode film. The second pixel electrode film and the first pixel electrode film are etched in turn using the photoresist pattern 95 as a mask. Subsequently, the photoresist pattern 95 is removed. Thus, a pixel electrode 25 consisting of the second pixel electrode 22 and the first pixel electrode 21 is formed. Etching the second pixel electrode film and the first pixel electrode film in turn is generally performed by using a wet etching solution, and the photoresist pattern 95 is removed by using a stripping solution.
In the meantime, a galvanic phenomenon occurs when two materials whose electromotive forces are different are simultaneously exposed to an electrolyte solution. As a result, the material having the greater electromotive force is corroded.
In general, since the first pixel electrode 21 is a reflecting electrode and the second pixel electrode 22 is a transparent electrode, the pixel electrodes 21, 22 are formed by using different materials. Accordingly, electromotive forces of the pixel electrodes 21, 22 can be different. Consequently, the galvanic phenomenon occurs between the first pixel electrode 21 and the second pixel electrode 22 when the first pixel electrode 21 and the second pixel electrode 22 are simultaneously exposed to the etching solution or the stripping solution, that is, the electrolyte solution. As a result, an electrode having the greater electromotive force between the second pixel electrode 22 and the first pixel electrode 21 is corroded, resulting in a break down of the films of the pixel electrode 25.